In the medical field it is frequently necessary after surgery or after a patient has incurred a trauma to the chest cavity to collect fluids from the chest cavity after the cavity has been closed. This type of fluid collection is commonly referred to as "closed-wound drainage". One particularly important feature of closed-wound drainage is that it requires a relatively low vacuum to suction fluids from the patient's chest cavity. If higher vacuums are used, damage to the internal organs may occur. Typical vacuum ranges of between 20-30 cm. H.sub.2 O are used to collect fluids from a closed chest or pleural cavity. However, in most hospitals, the vacuum sources commonly available are in the range of 0-760 mm. Hg. Most hospitals provide such vacuum sources on the wall next to a patient's bed. It is therefore necessary to provide a system which converts a relatively high vacuum provided by the hospital to a relatively low vacuum for use in closedwound drainage systems. It has been found that the vacuum source provided at a patient's bedside in many hospitals may also be a variable pressure vacuum source. With such sources, the vacuum provided may vary unexpectedly. Therefore, a need exists to provide a system which will not only convert a relatively high vacuum to a low vacuum but will also maintain a relatively constant vacuum despite fluctuations that may occur in the high vacuum source.
Another need exists in draining fluids and gases from a patient's pleural cavity in that it is important that as the gases are removed from a patient that they are not inadvertently returned to the patient. Typically, in a closed-wound drainage system, a small amount of gas is removed from the patient's pleural cavity with each inhalation of the patient. If the patient's lung is collapsed, each time a small amount of fluid and gas is removed from the patient's pleural cavity, the patient's lung is allowed to expand by the amount of fluid or gas that is removed. Thus, the patient's lung will typically gradually expand over a period of several days if the lung has entirely collapsed. During this process, it is important to make sure that gases are not inadvertently returned to the patient which would cause the lung to re-collapse.
Air may be inadvertently returned to a patient's pleural cavity when it is necessary to transport a patient from one location to another. When a patient is transported, it is frequently necessary to disconnect the patient from a vacuum source that is fixed in the wall of a hospital. The patient is then allowed to drain fluids from the pleural cavity using only gravity. Under such conditions, fluid will continue to drain, but air may return to the patient if air is present within the closed-wound drainage system. Therefore, it is necessary to provide a one-way check valve to prevent such return of air. One object of the present invention is to provide such a one-way check valve in a stand-alone module.
Another object of the invention is to provide a water-based stand-alone module which can be used not only for pleural wound drainage systems, but can be also be used for other drainage applications such as knee and hip surgery.